The present invention relates to a test fixture to be used in determining the resiliency of a cylindrical sample of a material, such resiliency being indicated by the diametric deflection of the sample under a dynamic load. In particular, the test fixture relates to a transducer frame engageable with the sample and to a mechanism that aligns the sample and frame for properly receiving the dynamic load along a force-applying axis. The device has particular application in measuring the resiliency of cylindrical samples of asphalt materials.
As disclosed in Schmidt, U.S. Pat. No. 3,854,328, the resiliency of a sample may be determined by applying an impulsive compressive force to the sample and measuring the resulting diametric deflection induced by the force. As Schmidt further discloses, although the transducer used to sense the deflection could be mounted on the base of a testing device, it is preferable to mount the transducer on a frame which is carried by the sample throughout the period of deflection. The transducer, then, will properly measure the diametric deflection without tangential slippage across the curved surface of the sample, as might occur were the transducer to be affixed to the base.
As shown in Schmidt, it has been customary to secure the frame to the sample by two pairs of thumb screws, one pair for engaging each of the flat end faces of the cylindrical sample. To assure proper positioning of the transducers, so that the transducers lie in a measurement plane containing the cylindrical axis of the sample, it is necessary to properly position the frame on the sample. For this purpose, a special stand has been employed into which the sample is placed and on which the frame is rested while the frame thumb screws are individually turned for engagement with the sample. However, when many samples require test, much valuable staff time is consumed by this frame orientation and engagement procedure, particularly since each thumb screw must be individually turned. Furthermore, after the frame is properly secured to the sample, each sample must then be individually oriented with the respective top and bottom loading faces so that the cylindrical axis of the sample lies substantially normal to, and aligned with, the force-applying axis, as well as parallel to the contacting edges of the loading face. Without attention to these relationships, the force-applying axis may be misaligned in relation to the frame, or the respective loading faces may be presented with variable sample surface areas during deflection, thereby distorting applied stress readings. Yet the attention that must be paid to individual orientation procedures greatly extends the test time required for each sample. To further aggravate this problem, the resiliency of any one sample is commonly measured along two axis of the sample, each perpendicular to the other, thus doubling the required set-up times.
What is required, then, is a test fixture that will measure the diametric deflection of many samples successively without a large time expenditure for individual frame and sample orientation and engagement.